According to the prior art, traditional dampers comprise a cylinder containing a damping fluid, at least one piston translatable within said cylinder and defining two damping chambers, and at least one rod for controlling the movement of said at least one piston within said cylinder. In addition, these devices have one or more narrow passages obtained between the piston and/or the cylinder and/or the rod for allowing said damping fluid to be forcedly moved from one to the other of said two damping chambers when said piston is controllably moved within the cylinder in both the directions of movement. In this way, when the speed of the rod exceeds a certain preset threshold value, the stroke of the piston, and therefore of the rod, can be slowed down by occluding one or more narrow passages on the basis of the speed of the damper rod while the piston is running within the cylinder. According to the prior art, International Application WO2005/045278 describes a damper which allows the speed of the control rod to be reduced when a certain forward speed thereof is exceeded. In fact, in this patent application, the piston has a plurality of side narrow passages, or grooves, spaced from each other, and it is equipped with a disc integral with the piston but rotatable and translatable with respect thereto and provided with a corresponding plurality of passages spaced from each other. Such a disc is rotated with respect to the piston on the basis of both the forward direction and the movement speed of the rod so as to move the above mentioned passages away from the above mentioned narrow passages or grooves of the piston as the speed of the rod is increased. Thus, the section provided by the narrow passages for the dumping fluid passing therethrough is reduced, thereby increasing the resistance against the passage of said fluid and consequently slowing the rod.
In these dampers, therefore, the resistance provided by one or more narrow passages is changed according to the speed of the rod so as to reduce the speed of the latter in case of a sudden acceleration thereof such as, for example, when the rod is subjected to an excessive external force. For example, this is the case when the door of the oven is closed with an excessive force, leading to the risk of a great, dangerous impact of the door itself against the abutment portion of the oven.
However, the dampers of the prior art are not free of drawbacks. In fact, these dampers are quite complex from a constructional point of view, and therefore, their assembly is time-consuming and requires a considerable accuracy.
Accordingly, an object of the present invention is to provide a damper which, in addition to be able to reduce automatically the speed of the rod when the external force acting thereon is suddenly increased, is also structurally simple.
Another object of the present invention is to provide a damper which is also functionally simpler than those of the prior art.